A litz conductor is an electrical conductor that consists of thin individual wires and is therefore easy to bend. The up to several hundred individual wires of the litz are mostly enclosed in a common insulating sheath.
Litz conductors are primarily used where frequent movements or shaking loads occur—for example, machines, motor vehicles and aircraft and robots—or where a mobile device must be provided, as for example electrical hand tools, network connections capable of being plugged in, or microphone and speaker cables. Depending on the requisite flexibility and degree of loading, litz conductors are used with thin or ultra-thin wires.
In particular applications, the conductors are packaged, that is, provided with multi-core cable ends, cable shoes, plug connections or the like.
This packaging is customarily undertaken using so-called crimping. With this, a force-locked, homogeneous, undetachable connection is made between the conductor and the connecting element, which ensures a high level of electrical and mechanical safety. Generally, where it is not easy to lay a pre-packaged cable, the cable alone is laid to the target location, and only there is an electrical contact piece attached, mostly by crimping, to the end of the lead. With the aid of crimping pliers, the plug and cable are connected in a force-locked fashion, mostly with a first crimping connection generated in the insulated area and a second crimping connection at the insulated end of the cable to produce the electrical connection.
Along with connection safety, crimping also achieves considerable simplification in handling. The connection is produced by pressure, with tuned crimp profiles causing a precisely preset deformation of the connecting element and lead precisely at the connecting piece and lead cross section.
If cables are packaged only after being laid, i.e., provided with the requisite connections, then, especially in large wire harnesses with many different line cross sections, the result can be that on-site technical personnel may not be able to choose suitable crimping profiles for the particular cables or litzes, especially because, with the smaller lead cross sections, it simply may not be possible to scrutinize the result to assess the lead cross section.
The results are either electrical and/or mechanical connections that are too loose and become detached on their own, or incomplete crimp connections, in which a part of the litz conductor not connected in form-locked fashion with the contact untangles, which under certain circumstances may lead to short circuits in the wire harness.
Using, for example, a vernier to measure the diameter of the lead produces erroneous readings due to the mobility of the litz conductor; the individual wires are pushed against each other and compressed flat by the legs of the vernier, so that it is not possible to precisely determine the cross-sectional area.
Measurement of the diameter of the lead with insulation would be possible, but cannot necessarily be inferred from the lead cross section, because insulation may have varied thicknesses with different types of leads.
U.S. Pat. No. 2,374,830 A discloses a measuring gauge for determining the thickness of knitting needles and other objects having a circular cross section. The measuring gauge consists of a housing with a tapered spigot slot through which the object can be run. The display comprises a scale and a display element which is pressed using a spring against the object to be measured, to allow a readout of the diameter on the scale.
JP 04-118501A represents a solution for checking the cross-sectional form of an object. The measuring instrument consists of an upper and lower measuring strip, between which the measured object is placed, with measurement conducted by two interlocking contact surfaces in the tool.